Rheostat potentiometer and method



TRUCTING THE SAME June 1l, 1935. D. T. SIL-:GEL

RHEOSTAT POTENTIOMETER AND METHOD OF CONS Original Filed March 4. 1932iii Ressued June l11, 1935 UNITED STATES RHEOSTAT POTENTIOMETER ANDMETHOD F CONSTRUCTING THE Sm David T. Siegel, Chicago, Ill.

Original No. 1,942,495,

Serial No. 596,787, March 4, for reissue November '1, 1934, Serial No.

Claims.

'Ihis invention relates to improved resistance devices, particularlypotentiometers or rheostats, comprising a dielectric structure in whichthe base and wound core are fused into an integral unit.

The main object of my improved device is to provide a unit structure inwhich the base becomes an integral part of the core, increasing theeffective radiating surface for ,the dissipation of the heat generated;and further to provide a structure in which the resistance element staysin fixed position independent of its expansion; to provide a core whichcan be wound in equal or progressive sizes of wire and later fused intoa unit ceramic structure with a base; to provide a heat treatment informing the unit structure which stabilizes the resistance; to provide astructure which is rigid and forms a protection for the resistanceelement; to provide contacting surfaces on a resistance element embeddedin a ceramic structure; to provide an improved contact maker capable ofmaintaining a clean smooth surf ace on the resistance wire; to providein the ceramic structure limits to the swing of the sweeper arm; toprovide a self-adjusting non-arcing brush or contactor; and to provideimproved means for maintaining efficient electrical connection. betweenthe resistance wire and the contacter arm.

An illustrative embodiment of my invention is shown in the accompanyingdrawing in which;

Figure l is a plan View of a porcelain base forming part of theresistance device.

Fig. 2 is a plan view of a porcelain core with metal terminals attachedand windings shown in part.

Fig. 3 is a plan view of a porcelain base with the core seated in place.

Fig. 4 is a section taken on the line 4-4 of Fig. 3, showing the core indotted lines.

Fig. 5 is a section on the line 5--5 of Fig. 2.

Fig. 6 is a plan view of a complete assembly of a potentiometerrheostat.

Fig. 'l is a cross section on the line 1-1 of Fig. 6.

In the form of my improved rheostat shown, the unit ceramic part isconstructed by assembling a circular porcelain base I and a splitporcelain ring 2 having flattened sides. A seat for the split or cutoutring 2 is formed in the base I by a ledge 3, a cone-shaped raised center4, and a radial raised arm.

The cut-out ring 2 is uniformly wound with resistance wire 6. Copperterminals 1 surround the ends of the core 2, and the ends are brazed tothe resistance wire Ii. Fusible ceramic material Il, shown in Fig. 7,fills the seat and covers the entire cutout ring 2, including the wire6. and termidated January 9, 1934, 1932. Application '151.917

nal 1. By the term fusible ceramic material I refer to the substancecommonly used for coating ceramic products and known in the trade as avitreous enamel slip or flux; and the term as used in the claims shouldbe so understood. The cutout ring 2 is then placed in its seat, with thecontacting surfaces 9 uppermost. When seated, a part of the resistance 6contacts with the base I.

The commutation or contacting surfaces 9 and the punched ends Ill of theterminal 1 are then wiped clean and the combination is placed in aceramic furnace, where the ceramic material 8 is fused. After theceramic unit with embedded wires is formed, the contacting surfaces 9are polished smooth, and the terminals Ill are ground and solder-dipped.

Through the center of the cone 4 is a central aperture I I, in which isfitted a metal bushing I2, externally threaded to receive a lock-nut I3,and

provided at the opposite end with a thrust bearing I4. The thrustbearing I4 co-acts with a metal connecting strip I5, which extends fromthe center of the cone 4 over the raised arm 5, forming an electricalterminal I6.

The movable parts of the rheostat comprise a shaft I1, which is seatedin the metal bushing I2. One end of the shaft I1 is shouldered andsquared to receive a slotted sweep arm I8, which is riveted to the shaftI1. Threaded on the shaft l1 is a spring washer I9 arranged to maintainfixed tension between the sweep arm I8 and the fixed metal bushing I2and a circular groove 20 is cut in the shaft I1 to receive a thrustwasher 2| which co-acts with the threaded end of the metal bushing I2.

A control knob 22 is fastened to the projecting end of the shaft I1 by aset screw 23, which contacts with a plane surface 24 on the shaft Il.The outer end of the sweep arm I8 is bent to form a mechanical guard 25for an independent carbon graphite button 26, which rides on thecontacting surface 9.

The mechanical guard 25 is punched to form an aperture at the bend. Thecarbon graphite button 26 is seated in a crown top metal casing 21 andsoldered to the metal casing 21 is a flexible cable 28, which iselectrically connected to the sweep arm I8 by a rivet 29. The rivet 25also fastens a double bend steel spring 30 to the sweep arm I8. The freeend of the spring 3U has two apertures, through which the cable 2B isthreaded in such manner that the crowned casing 2l of the graphitebutton is normally held under spring tension on the contacting surfacethrough what is substantially a ball and socket joint. The spring 30passes through the aperture 32, punched in the sweeper arm I8, and thepunching 33 forms a stop for the arm through contact with the radial rib5.

In operation the carbon graphite button rides on the polished contactingsurfaces oi' the turns of the resistance wire and the tension betweenthe button and the resistance wire is maintained substantially constantat all positions.

With my construction the control knob gives positive control of thelocation of the graphite button on the resistance wire, and the ball andsocket-like mounting of the button assures positive contact with theresistance wire even though the wire and button both become worn.Experience has proved that a carbon graphite button with free seating,as here provided, and under tension, does not tend to abrade theresistance wires, and since the button bridges several wires, there isno destructive arcing at the contacting surface.

In my improved construction, the cable 28 carries substantially all thecurrent passing through the device, thus preventing heating of thespring and deterioration of the spring temper, and one of the advantagesof my construction is the formation of. a compact unit, in which theheat generated is dissipated by the entire surface of the structureforming the mounting, thus maintaining under load, a comparatively lowtemperature.

Another important advantage of my improved construction lies in the factthat each turn of the resistance wire wound upon the supporting core issolidly backed throughout the entire length of its convolution and inthe baking process each individual turn of the resistance element issolidly and entirely fused onto the supporting core which backs it up.On the under side of the core the resistance wire is also fused both tothe core and to the base upon which the core is mounted. Thus each turnof the resistance element is securely fastened to the core and can in noway be displaced laterally under the sliding action of the contactorelement. Regardless of the expansion of the resistance wire, that isusually resultant as the element is heated in operation, the possibilityof the individual turns of wire being moved so as to vary the setting ofthe control knob for any certain resistance is entirely eliminated.

Although but one specific embodiment of this invention has been hereinshown and described, it will be understood that certain details of theconstruction shown may be altered or omitted without departing from thespirit of this invention as dened in the following claims.

I claim:

l. The process of making a resistance device in forming a ceramic core,tightthroughout said limited portion to provide an extended area oi barewire, locating the wound core in its position on the base, and bakingthe assembly to fuse the said material and to permanently Join the coreto the base and the resistance Wire to the core.

2. The process of making a resistance device which consists in forming aceramic core, tightly winding a resistance wire upon said core, securinga terminal to said core and brazing the to said resistance wire,

of the base with a fusible ceramic material, removing the said materialfrom a limited portion of the wound core whereby to expose the topsurfaces of the wire throughout said limited portion to provide anextended area of bare wire, locating the wound core in its position onthe base, and baking the assembly to fuse the said material and topermanently join the core to the base and the resistance wire to thecore.

3. The process of making a resistance device which consists in tightlywinding a resistance wire upon a suitable ceramic core, providing aceramic base grooved to receive the wound core, coating the Wound coreand the groove of the gether and the resistance wire is entirely andimmovably fused to the core.

4. A resistance device, comprising, in combif:

nation, a core of arcuate outline, said core beengagement with said 5. Aresistance device comprising, in combination, a generally circular,ceramic core, a resistance Wire on said core, a the core and permanentlyjoined to an end of said Wire, a ceramic base on which said core ismounted, and a baked, fusible ceramic material covering said core,terminal mounting and the surface of said base on which said core ismount- DAVID T. SIEGEL.

terminal secured on

